Vehicle state determination integrity

ABSTRACT

A vehicle includes a semi-active suspension including suspension dampers controllably adjustable in accordance with electronic stability control commands and ride and handling commands. Vehicle steering response states, turning direction states and vehicle dynamics states are binary coded in respective state variables and suspension control calibrations are binary coded in calibration words. Integrity and security of state variables and calibration words are ensured in efficient binary digit resource allocation schemes.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention is related to commonly assigned and co-pendingU.S. patent application Ser. No. 11/157,208 filed on even date herewith.

TECHNICAL FIELD

The present invention is generally related to vehicle stability control.More particularly, the invention relates to data integrity andflexibility of vehicle state determinations used in such control.

BACKGROUND OF THE INVENTION

Steering stability and performance of a vehicle are largelycharacterized by the vehicle's understeer and oversteer behavior. Thevehicle is in an understeer condition if the vehicle yaw is less thanthe operator steering input, where turning the steering wheel more doesnot correct the understeer condition because the wheels are saturated.The vehicle is in an oversteer condition if the vehicle yaw is greaterthan the operator steering input. Surfaces such as wet or unevenpavement, ice, snow or gravel also present vehicle stability andhandling challenges to the operator. Similarly, in a panic or emergencysituation, such as during obstacle avoidance, an operator may react byapplying too much steering or failing to counter-steer to bring thevehicle back to its intended path. In any of these cases, the actualvehicle steering path deviates from the intended steering path.

Vehicle stability controls have progressed from first generation systemsbased upon braking and traction control (braking and powertrain torquemanagement) technologies to more recent systems including independentand coordinated controls of brake, powertrain, steering and suspensiondamping sub-systems. Typically, distributed control modules are employedto directly interface with respective actuators to effect the desiredsub-system controls. Coordination and authority of such sub-systemcontrol may be handled by way of a supervisory control.

Braking and traction control sub-systems can effect understeer andoversteer stability enhancements. Such sub-systems rely on wheel speed,steering angle, vehicle speed, yaw rate and other considerations toreduce engine torque and apply vehicle braking to maintain the vehicletravel along the intended path.

Active front steering sub-systems can effect understeer and oversteerstability enhancements. Such sub-systems employ a steering actuatorsystem that relies upon an operator intended steering input from a handwheel sensor, vehicle speed, vehicle yaw rate and other considerations,and provides a correction to the operator steering input to cause thevehicle to more closely follow the vehicle operator's intended steeringpath to increase vehicle stability and improve vehicle handling.

Semi-active suspension systems are also incorporated into some modernvehicles and are generally characterized by dampers that are controlledto change the suspension characteristics of the vehicle based on roadconditions, vehicle speed, yaw rate and other considerations. Variablefluid-based dampers are known having discrete damping states andcontinuously variable damping states which affect both jounce andrebound response of the suspension system. Variability in damping may beattained by variable orifice devices or controlled viscosity fluids(e.g., magnetorheological (MR) or electrorheological (ER)) within thedamping device. Variable dampers are used predominantly to achieve lowspeed ride comfort and high speed handling enhancement (ride andhandling). However, variable damping techniques are known to enhancevehicle stability in certain understeer and oversteer situations and maybe implemented as part of an overall vehicle stability control.

Whether implemented independently, overlapped or integrated, braking,traction, steering and suspension-based stability enhancementsub-systems all rely upon certain common vehicle level parameters. And,vehicle dynamics information, including vehicle steering response (e.g.,understeer, oversteer or neutral steer), vehicle turning direction(e.g., left or right) or combinations thereof, defining vehicle dynamicsstates is commonly employed across stability enhancing sub-systems.Effective stability control systems, therefore, benefit from integrityand flexibility of use of such vehicle dynamics information.

Systematic reuse of control components—both within a vehicle's controlarchitecture and across vehicle platforms and applications—promoteslow-cost, quick-to-market and widely available vehicle systems.Significant benefits result directly from the application developmentcost, time, validation, maintainability and flexibility advantagesafforded by such common control assets. Therefore, it is desirable thata vehicle stability enhancement system be characterized by a high degreeof control component availability and access to enable and promotereuse, maintainability, common validation and development, cost and timesavings and multi-platform utilization.

SUMMARY OF THE INVENTION

In accordance with various aspects of the present invention, a vehicleincludes a computer based controller for effecting vehicle stabilityenhancement in response to certain driving conditions through responsivecontrol of vehicle sub-system actuators. Apparatus is provided forindicating vehicle driving conditions and includes a memory devicehaving predetermined bit positions for storing binary codes of apredetermined bit length and a plurality of valid binary codescorresponding to a plurality of vehicle driving conditions. Each validbinary code is characterized by a predetermined ratio of correspondingbit states and is differentiated from all other valid binary codes bydifferences between at least two complementary bits of each respectivevalid binary code. In accordance with one aspect of the invention, theplurality of vehicle driving conditions include oversteer and understeerand the predetermined bit length is two bits. In accordance with anotheraspect of the present invention, the plurality of vehicle drivingconditions includes oversteer, understeer and neutral steer and thepredetermined bit length includes three bits. In accordance with anotheraspect of the present invention, the plurality of vehicle drivingconditions includes left and right turning and the predetermined bitlength includes two bits. In accordance with another aspect of thepresent invention, the plurality of vehicle driving conditions includesoversteer-left, oversteer-right, understeer-left and understeer-rightand the predetermined bit length comprises four bits. In accordance withanother aspect of the present invention, the plurality of vehicledriving conditions includes oversteer-left, oversteer-right,understeer-left, understeer-right, neutral steer-left and neutralsteer-right and the predetermined bit length includes four bits.

A method for indicating vehicle driving condition states within a memorystructure of the computer based controller includes providing a firstbinary coded variable for conveying vehicle steering response stateswherein valid binary codes share a first ratio of individual bit statesand are differentiated one from another by differences between at leasttwo complementary bits. Also included in the method is providing asecond binary coded variable for conveying vehicle turning directionstates wherein valid binary codes share a second ratio of individual bitstates and are differentiated one from another by differences between atleast two complementary bits. And, also provided is a third binary codedvariable for conveying vehicle dynamics states based on combinations ofvehicle steering response and turning direction states wherein validbinary codes share a third ratio of individual bit states and aredifferentiated one from another by differences between at least twocomplementary bits. In accordance with one aspect of the presentinvention, vehicle steering response states include oversteer andundersteer and the first binary coded variable is two bits. Inaccordance with another aspect of the present invention, vehiclesteering response states include oversteer, understeer and neutral steerand the first binary coded variable is three bits. In accordance withanother aspect of the present invention, vehicle turning directionstates include left and right and the second binary coded variable istwo bits. In accordance with another aspect of the present invention,vehicle dynamics states include oversteer-left, oversteer-right,understeer-left and understeer-right and the third binary coded variableis four bits. In accordance with another aspect of the presentinvention, vehicle dynamics states include oversteer-left,oversteer-right, understeer-left, understeer-right, neutral steer-leftand neutral steer-right and the third binary coded variable includesfour bits.

These and other advantages and features of the invention will becomeapparent from the following description, claims and figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block schematic diagram illustrating a vehicle architecturesuitable for implementing vehicle stability control embodying thepresent invention;

FIG. 2 is a chart illustrating exemplary valid bit positional patternsof variables embodied in a memory device for indicating vehicle steeringresponse states in accordance with the present invention;

FIG. 3 is a chart illustrating exemplary valid bit positional patternsof a variable embodied in a memory device for indicating vehicle turningdirection states in accordance with the present invention;

FIG. 4 is a chart illustrating exemplary valid bit positional patternsof a variable embodied in a memory device for indicating vehicledynamics states in accordance with the present invention;

FIG. 5 is a flow chart representing exemplary functions executed in oneor more computer based controllers in carrying out the method of thepresent invention;

FIG. 6 is a chart illustrating exemplary valid bit positional patternsfor individual jounce and rebound control calibrations for each of fourexemplary vehicle dynamics states at each of four exemplaryindependently controllable suspension units in accordance with thepresent invention; and

FIG. 7 is a matrix illustrating critical and non-critical vehicle cornerand damper motion-combinations in accordance with vehicle turningdirection.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A vehicle stability control system 12 is schematically illustrated inFIG. 1 and includes vehicle 11 and vehicle stability enhancementcontroller (supervisory controller) 10. A plurality of actuators 19associated with various vehicle sub-systems effect various forces uponvehicle 11 to enhance stability and maintain an intended path inresponse to such inputs as steering wheel angle, vehicle speed, wheelspeed and vehicle yaw rate, among others. For example, in an activefront steering system, the steering angle of the front vehicle wheels isaffected by way of a steering actuator sub-system that is commanded toeffect the desired vehicle stability enhancement. In abraking/powertrain vehicle stability enhancement sub-system, individualwheel braking and powertrain torque may be affected by way of modulatedhydraulic brake pressure and engine output torque control through avariety of well-known techniques (e.g., spark timing, cylinderdeactivation, engine fueling, etc.). In a semi-active suspensionsub-system, suspension damping characteristics may be altered in amanner to effect a desired vehicle stability enhancement. Other systems,including but not limited to active suspensions wherein spring rates arealterable, and active rear steering wherein rear wheel steering angle isalterable, are equally within the scope of application of the presentinvention.

Each such vehicle sub-system has associated therewith one or moresub-system control modules 14. Control modules are standard automotivecomputer-based devices with standard control and logic circuitry whichmay include a micro-controller including arithmetic logic unit (ALU) andmemory devices including read-write or random access memory device(RAM), read-only memory (ROM) devices in which are stored a plurality ofroutines for carrying out sub-system control and diagnostic operations,including routines for carrying out operations for implementing variousaspects of the present invention. Each routine includes a sequence ofinstructions that are executed by a microprocessor followingpre-established events or interrupts or on a timed basis such as instandard executory loops. Such control modules are generally well knownto those skilled in the art.

Vehicle sub-systems are operable in a distributed control fashionwherein each of the control modules 14 associated with a particularsub-system is responsible for normal control functions thereof bycommanding the control of the respective sub-system actuators 19. Suchnormal control functions generally are not related to vehicle dynamicscontrol other than in a passive, contributory sense. Engine controller15, for example, is responsible for effecting an amount of output torquein response to an operator demand and for torque management during ratioshifting of a multi-speed ratio automatic transmission. The enginecontroller also normally performs emission critical and fuel economycritical functions which may implicate spark timing, cylinderdeactivation, engine fueling, etc. Brake controller 21 is normallyresponsible for brake application in accordance with operator appliedbrake pedal pressure and anti-lock modulation in accordance withindependent and comparative wheel speed measurements. Steeringcontroller 17 is responsible for variable assist—reducing steeringeffort during low speed and parking maneuvers and progressivelyincreasing steering effort as vehicle speed increases. A four wheelsteering control is also responsible for controlling the turn angle ofthe rear wheels in the opposite direction from the front wheels at lowvehicle speeds and in the same direction at higher vehicle speeds. Adamper controller 25 likewise is responsible for tuning the ridecharacteristics of the vehicle in accordance with vehicle speed,predominantly for operator comfort through reduced damping at lowvehicle speeds and for improved highway feel through increased dampingat higher vehicle speeds.

The vehicle 11, sub-system actuators 19 and sub-system controllers 14all provide various input signals 16 to the supervisory controller 10for use in vehicle stability enhancement routines. Vehicle inputs mayinclude, for example, yaw rate, lateral acceleration and vehicle speed.Actuator inputs may include, for example, damper position and road wheelangle. Sub-system controller inputs may include, for example, individualbrake corner actuation override, brake system blending terms, shockdamping value override, active front steering actuator override or extrasteering angle. Vehicle 11, sub-system actuators 19 and sub-systemcontrollers 14 input signals may be provided over controller areanetwork (CAN) bus 18, but may take the form of discrete sensor signalinputs, serial communication lines, etc. Supervisory controller 10 inturn provides high priority control commands over CAN bus 18 foroverriding, modifying or adapting the normal control of the sub-systemcontrollers 14 in the interest of implementing vehicle stabilityenhancing control of the various sub-system actuators 19.

Supervisory controller 10 may include lower-level supervisorycontrollers (not separately shown) corresponding to the variousstability enhancing sub-systems (e.g., wheel torque (i.e., brake &engine torque) supervisor, steering supervisor and suspensionsupervisor) and oversees the coordination of these various stabilityenhancing control sub-system supervisors. The various sub-systemcontrols, collectively or individually, in accordance with a particularvehicle application, are generally referred to as electronic stabilitycontrol and illustrated as functionally related to supervisorycontroller 10 as ESC.

The schematic block diagram of FIG. 1 includes more detailedillustration of an exemplary suspension damper control sub-system 20 inaccordance with the present invention. The system includes dampercontroller 25 and a plurality of suspension dampers 13 individuallyassociated with the respective suspension corners of the vehicle 11.Damper control sub-system 20 includes the normal control functionsgenerally referred to as ride and handling, illustrated as functionallyrelated to damper controller 25 as R&H. The vehicle 11 provides aplurality of signals from sensors or derivations, including vehicle yawrate, vehicle lateral acceleration, vehicle speed, steering wheel angleand individual damper positions. The plurality of suspension dampers 13includes, in the present example of a conventional four wheel positionvehicle, at least one suspension damper corresponding to each corner ofthe vehicle. These corners are referred to positionally and arecorrespondingly labeled in FIG. 1 as right-front (RF), left-front (LF),right-rear (RR) and left-rear (LR). Each damper effects a damping forceupon vehicle 11 in accordance with damper commands, for example controlcurrents for effecting a desired damping response in an MR based damper.

Generally under normal vehicle operation, suspension control ispreferably provided in accordance with normal ride and handling (R&H)objectives, and open open-loop controls are employed wherein all thedampers at each corner of the vehicle are controlled relative to inputssuch as lateral acceleration, vehicle speed, steering wheel angle anddamper position. Such open loop controls are effective during lineardriving conditions (e.g., substantially neutral oversteer/understeercondition). One skilled in the art will appreciate that such controlsare generally designed to effect a baseline total vehicle damping andbaseline distribution thereof to each vehicle corner. Total vehicledamping force generally increases with increasing vehicle velocity anddecreases with decreasing vehicle velocity to effect R&H objectives.Additionally, redistribution of the total vehicle damping force will beeffected based substantially upon steering input. Such normal R&H dampercontrol commands are, as described hereinabove, determined by dampercontroller and implemented thereby, for example, as current controlcommands issued to each of the RF, LF, RR and LR damper actuators inaccordance with a R&H calibration as further described hereinbelow.

Non-linear driving conditions wherein vehicle oversteer or understeerbehavior or a transitional neutral steer behavior out of or intermediateoversteer and understeer states are determined and counteracted by ESCcontrols of the supervisory controller 10. Such ESC control includespreferential implementation of closed-loop active damper control of someor all of the vehicle corner dampers. ESC damper control is effective todetermine an effective total vehicle damping, and front-to-rear andside-to-side distributions thereof. One skilled in the art willrecognize that understeer behavior can be improved with a dampingdistribution weighted toward the rear of the vehicle and that oversteerbehavior can be improved with a damping distribution weighted toward thefront of the vehicle. Furthermore, certain of the vehicle corner anddamper motion combinations may be determined critical in accordance withthe vehicle turning direction and benefiting from such ESC dampercontrol whereas certain of the vehicle corner and damper motioncombinations may be determined non-critical in accordance with thevehicle turning direction and may be adequately controlled in accordancewith normal ride and handling objectives with the R&H controls. ESCdamper control commands are determined by supervisory controller 10 andimplemented by the damper controller 25, for example, as current controlcommands issued to each of the RF, LF, RR and LR damper actuators inaccordance with a ESC calibration as further described hereinbelow.

In a preferred embodiment, the R&H controls will be used to command thedamping force of the non-critical vehicle corner and damper motioncombinations. And, the ESC damper controls will be used to command thedamping force of the critical vehicle corner and damper motioncombinations. Therefore, during normal linear driving conditions, allvehicle corner damper and damper direction combinations are preferablycontrolled in accordance with a purely R&H calibration wherein the R&Hcontrol commands determined by damper controller 25 are provided to therespective damper actuators. During non-linear driving conditions,including oversteer, understeer and transitional neutral steerconditions, all vehicle corner damper and damper direction combinationsare preferably controlled in accordance with a ESC calibration whereinthe R&H control commands determined by damper controller 25 are providedto the respective damper actuators for non-critical vehicle corner anddamper motion combinations whereas the ESC control commands determinedby supervisory controller 10 are provided to the respective damperactuators for critical vehicle corner and damper motion combinations.The Matrix of FIG. 7 illustrates the critical and non-critical vehiclecorner and damper motion combinations in accordance with vehicle turningdirection. By the present invention, the ESC damper control isimplemented on the dampers and in the direction of damper motioncritical to the yaw dynamics of the vehicle thereby minimizing theeffects of such control on potentially destabilizing wheel controlevents which may occur during the application of other ESC controlsub-systems, e.g., wheel torque control and active steering, ordisruptive road input.

FIG. 5 illustrates functions carried out in the supervisory controller10 and the damper controller 25 in effecting the controls of the presentinvention. Therein is illustrated the determination of the vehicle'ssteering response, e.g., oversteer, understeer, neutral steer, and thevehicle's turning direction [block 501]. Next shown is setting of statevariable for the vehicle steering response state and turning state asdetermined [block 503]. Variables are generally understood in the art tocorrespond to assigned and addressable memory locations or registerswithin dynamic memory modules of the controllers, e.g., random accessmemory, and may comprise one or more bits of such multi-bit memorylocations. At various steps within the processes carried out by thecontrollers 10 and 25, validity checks are performed [block 505]relative to known good variable settings for the vehicle steeringresponse state and turning state-variables, for example as part ofexecutory diagnostic routines for the purpose of ensuring the integrityand security of the state data. Valid state variables result in thecontinuance of the present steps [block 5071 ] whereas invalid statevariables result in exiting of the routine in favor of additionaldiagnosis and/or recovery routines not further detailed herein.

Continuing under the assumption of validated vehicle steering responsestate and turning state variables [block 507], a vehicle dynamics statevariable is set corresponding to the vehicle steering response state andturning state. The vehicle dynamics state corresponds to the combinedturning direction and steering response and includes, at a minimum,oversteer-left, oversteer-right, understeer-left and understeer-right.The variable may further include neutral steer-left and neutralsteer-right representing transitional neutral steer conditions. Similarto the previously described validity checks performed upon the vehiclesteering response state and turning state variables, at various stepswithin the processes carried out by the controllers 10 and 25, validitychecks are performed [block 509] relative to known good variablesettings for the vehicle dynamics state variable, for example as part ofconventional executory diagnostic routines for the purpose of ensuringthe integrity and security of the state data. A valid state variableresults in the continuance of the present steps [block 511] whereasinvalid state variables result in exiting of the routine in favor ofadditional diagnosis and/or recovery routines not further detailedherein.

Continuing under the assumption of a validated vehicle dynamics statevariable [block 511], suspension damper calibrations are referenced as afunction of the validated vehicle dynamics state variable. Calibrationsare generally understood in the art to correspond to assigned andaddressable memory locations or registers within non-volatile memorymodules of the controllers, e.g., random object memory, and may compriseone or more bits of such multi-bit memory locations. Similar to thepreviously described validity checks performed upon the various vehiclestate variables, at various steps within the processes carried out bythe controllers 10 and 25, validity checks are performed [block 513]relative to known good calibration values for the suspension dampercalibrations, for example as part of executory diagnostic routines forthe purpose of ensuring the integrity: and security of the calibrationdata. A valid calibration results in the continuance of the presentsteps [block 515] whereas invalid calibrations result in exiting of theroutine in favor of additional diagnosis and/or recovery routines notfurther detailed herein. Continuing under the assumption of a validatedcalibration [block 515], damper control is implemented in accordancewith the referenced and validated calibration to effect the desireddamping commands at the vehicle corners.

A more detailed explanation of the functions set forth above withrespect to the illustration of FIG. 5, particularly with respect to dataintegrity and security aspects thereof, is now provided. Beginning firstwith the setting of state variable for the vehicle steering responsestate and turning state [block 503], FIGS. 2 and 3 are additionallyreferenced. The variable associated with steering response state isshown in FIG. 2 as including a two-bit position allocation in systemswherein neutral steer is not a utilized state. In systems whereinneutral steer is a utilized state, a three-bit position variable isallocated. Bit position allocations are preferably adjacent bits inlarger bit arrays, typically comprising 8, 16 or 32 bit words inaccordance with the controller employed architecture. Unutilized wordbits—for the purposes of the present variable definitions—are preferablyallocated to other variable usage and hence packed with othernon-related variable data not required to be further detailed herein. Inthe illustrated two-bit allocation scenarios shown in the chart of FIG.2, valid state variable values are illustrated. For each of the two- andthree-bit scenarios, valid variable values share a common ratio ofindividual bit states. In the two-bit allocation this ratio isone-to-one of “1s” and “0s”, whereas in the three-bit allocation thisratio is two-to-one of “1s” and “0s”. Furthermore, each of the validvariable values within each respective two- or three-bit allocation isdifferentiated from the others by differences between at least twocomplementary bits. In the two-bit allocation, there are only two bitsand each valid value comprises complementary bits. Therefore, the firstbit (taken from right to left) corresponding to the oversteer state “1”differs from the first bit corresponding to the understeer state “0”,and the second bit corresponding to the oversteer state “0” differs fromthe second bit corresponding to the understeer state “1”. Invalidvariable values for the two-bit steering response allocation include“00” and “11”. In the three-bit allocation, there are three bits andeach valid value comprises two pair groupings of complementary bits—thefirst and one of the second and third bits; the second and one of thefirst and third bits; and the third and one of the first and secondbits. The first and second position complementary bits of the understeervalue “110” both differ from the first and second position complementarybits of the oversteer value “101”. Similarly, the second and thirdposition complementary bits of the oversteer value “101” both differfrom the second and third position complementary bits of the neutralsteer value “011”. And, the first and third position complementary bitsof the understeer value “110” both differ from the first and thirdposition complementary bits of the neutral steer value “011”. Invalidvariable values for the three-bit steering response allocation include“000”, “001”, 010”, “100” and “111”. While the ratio of two-to-one of“1s” and “0s” respectively is exemplified, one skilled in the art willrecognize that the complementary or inverted arrangement using the ratioof two-to-one of “0s” and “1s”, respectively, is equally applicable.

The variable associated with turning response state is shown in FIG. 3as including a two-bit position allocation. Consistent with theconsiderations set forth hereinabove with respect to the steering statevariable, bit position allocations are preferably adjacent bits inlarger bit arrays, typically comprising 8, 16 or 32 bit words inaccordance with the controller employed architecture. Unutilized wordbits are preferably allocated to other variable usage and hence packedwith other non-related variable data. Valid state variable values areillustrated in FIG. 3 wherein valid variable values share a common ratioof individual bit states of one-to-one of “1s” and “0s”. Furthermore,each of the valid variable values is differentiated from the other bydifferences between these two complementary bits. Each valid valuecomprises complementary bits and, therefore, the first bit correspondingto the left turning state “1” differs from the first bit correspondingto the right state “0” and the second bit corresponding to the leftturning state “0” differs from the second bit corresponding to the rightstate “1”. Invalid variable values for the two-bit turning directionallocation include “00” and “11”.

Turning now to the setting of the variable associated with vehicledynamics state which comprises combinational information from validatedsteering response state, including transitional neutral steer, andturning direction state variables [block 507], FIG. 4 illustrates afour-bit position allocation. Consistent with the considerations setforth hereinabove with respect to the previously described individualstate variable for steering response and turning direction, bit positionallocations for the present vehicle dynamics state variable arepreferably adjacent bits in larger bit arrays (e.g., 8, 16 or 32 bitwords) in accordance with the controller employed architecture.Unutilized word bits are preferably allocated to other variable usageand hence packed with other non-related variable data. Valid statevariable values are illustrated wherein valid variable values share acommon ratio of individual bit states of two “1s” and two “0s”. In thefour-bit allocation, there are four bits and each valid value comprisesfour pair groupings of complementary bits—one of the bits of a firststate, e.g., “1”, paired individually with the two of the bits of thesecond state “0” and the other of the bits of the first state, e.g.,“1”, paired individually with the two of the bits of the second state“0”. Any valid vehicle dynamics variable value differs from any othervalid vehicle dynamics variable value by differences between at leasttwo complementary bits. For example, variable values corresponding toundersteer-left “0110” and understeer-right “1100” differ in such afashion with respect to the second and fourth position complementarybits. In a further example, variable values corresponding toundersteer-left “0110,” and neutral steer-left “1001” differ in such afashion with respect to the first, second, third and fourth positioncomplementary bits. All other valid binary coded values can be comparedin such a fashion to arrive at the same result. Invalid variable valuesfor the four-bit vehicle dynamics allocation include “0000”, “1111” andany four-bit combination having three bit positions written with either“0s” or “1s”.

Appreciated from the above description of the various individual andcombinatorial state variables is that valid binary coded variablesrequire compliance with a predetermined ratio of individual bit statesand differentiation one from another by differences between at least twocomplementary bits which effectively requires two bit transitions inopposite directions for a state change to be indicated. Furthermore, anadditional level of security is afforded to certain selected anomaloustransitions which may occur between valid values of state variables. Itis preferred that undesirable effects of anomalous transitions betweenvalid values of state variable be managed through design selection ofvalid values of the state variables such that predetermined undesirablestate transitions are avoided for the more common types of controllerrelated anomalies. For example, register shifting, including arithmeticlogic unit multiplication operations, and register inversion includingarithmetic logic unit one's complement operations, are common validoperations which if anomalistically performed can result in transitionof a state variable from one valid value to another valid value butwhich corresponding state transition represented thereby is unintendedand undesirable. In the present exemplary system, unintended oversteerstates, both with respect to vehicle steering response state variable(FIG. 2) and vehicle dynamics state variable (FIG. 4) are desirablyafforded the highest level of security whereby such previously describedanomalistic transitions among variable values will not result in thetransition the system into an oversteer state from a non-oversteerstate. In the present example, any oversteer state is the leastdesirable state to transition into in the event of an anomalistic statevariable change and is desirably afforded the highest level of security.Therefore, valid state variable values are chosen for oversteerconditions such that no two adjacent bit positions are the same (e.g.,adjacent bits are different). This is shown in the vehicle steeringresponse variable settings of FIG. 2 wherein the valid three bitvariable value for oversteer is “101”. This is also shown in the vehicledynamics state variable settings of FIG. 4 wherein the valid four bitvariable value for oversteer-left is “0101” and for or oversteer-rightis “1010”. Appreciated from such design selection is that the highestlevel of security against the described more common types of controllerrelated anomalies (e.g., register shifts and bit inversions). Hence, thepresent invention provides an otherwise unrealizable level of securityand integrity against bit, nibble, byte and word failures since each atleast two bits of a variable must change in opposite directions tosignify any state change. And, additional security can be providedagainst certain anomalistic state changes by selective assignment ofvalid sate variables. Such a scheme provides these benefits in anefficient binary digit resource allocation allowing for shared bitresource within the architected word structures of the computer basedcontrollers.

Having thus described the data integrity and security aspects of anelectronic stability control system suitable for implementation andapplication with any or all of a variety of individual stability controlsub-systems, e.g., wheel torque (i.e., brake & engine torque), steeringand suspension, the further aspect of calibration integrity particularlyrelevant to the implementation of damper suspension controls [515] isnow described with additional reference to the chart of FIG. 6. Alongthe top of the chart of FIG. 6 are columns differentiating, for a fourcorner vehicle, the eight vehicle corner and damper motion combinationscomprising LF jounce, LF rebound, RF jounce, RF rebound, LR jounce, LRrebound, RR jounce and RR rebound. Along the right side of the chart arerows differentiating four exemplary vehicle dynamic states as previouslydescribed as oversteer-left, oversteer-right, understeer-left andundersteer-right. For each of the eight vehicle corner and damper motioncombinations are two valid two-bit patterns comprising mutuallyexclusive calibrations for effecting either ESC control commands or R&Hcommands at the respective vehicle corner and damper motion combination.For example, an ordered two-bit pattern of “10” corresponds to acalibration indicative of the desirable control of the correspondingvehicle corner and damper motion combination in accordance with the ESCdetermined control commands. Similarly, the inverted ordered two-bitpattern of “01” corresponds to a calibration indicative of the desirablecontrol of the corresponding vehicle corner and damper motioncombination in accordance with the R&H determined control commands. Acomplete calibration corresponding to a particular vehicle dynamicsstate, for example oversteer left, comprises a 16-bit calibration wordincluding, for each vehicle corner and damper motion combination, one ofthe valid two-bit patterns. Thus, each defined vehicle dynamics statehas a corresponding calibration defining each vehicle corner and dampermotion combination control. Each of the eight vehicle corner and dampermotion combinations can be calibrated, in the present example, forcontrol with either of the ESC control commands or the R&H commands inaccordance with the designer and calibrator's desired objectives. Anadditional calibration corresponding to a pure R&H control—such as, forexample, where non-linear driving conditions are not present and do notrequire electronic stability enhancements—may similarly be provided andmay comprise a 16-bit calibration word wherein all individual two-bitpatterns are set to “01” to effect damper control in accordance with theR&H control commands exclusively. In a manner similar to the variousstate variables described hereinabove, valid calibrations can beconfirmed. The valid vehicle corner and damper motion combinationcalibration values are illustrated in FIG. 6 wherein valid calibrationvalues share a common ratio of individual bit states of one “1” and one“0”. Furthermore, each of the valid calibration values is differentiatedfrom the other by differences between these two complementary bits. Eachvalid value comprises complementary bits and, therefore, the first bitcorresponding to a ESC inactive (R&H active) calibration “1” differsfrom the first bit corresponding to the ESC active (R&H override) “0”and the second bit corresponding to the ESC inactive (R&H active) “0”differs from the second bit corresponding to the ESC active (R&Hoverride) “1”. Invalid calibration values for the two-bit calibrationallocation include “00” and “11”.

As an exemplary implementation of the calibration thus described, thedamper controller 25 is tasked with executing control commands, forexample current control of the damper actuators, that are eitherdetermined by control routines executed and carried out within theinstruction sets therein related to R&H control or determined by controlroutines executed and carried out within the instruction sets of thesupervisory controller 10 related to ESC control. Thus, data transfersbetween the supervisory controller 10 and the damper controller 25 occurincluding the transfer of ESC control commands and ESC calibrations. Thedamper controller is then tasked with interpreting the calibration andproviding the appropriate control commands, ESC or R&H, in accordancewith the individual vehicle corner and damper motion calibrationsprovided thereto. This scenario provides an example of the validationopportunities for the control to act upon the calibration whereinsubsequent to transfer to the damper controller 25 the calibration isvalidated with respect to known good calibration states.

An alternative implementation of calibrations as described includescalibrations that are derived in accordance with dynamic determinations.That is to say, individual vehicle corner and damper motion directioncalibration words may be determined on the fly as a function ofpredetermined vehicle operating parameters and stored in a read-writememory devices as opposed to-being predetermined, stored in anon-volatile memory device and later referenced as describedhereinabove. Such dynamic operations benefit to an even greater degreefrom the security and integrity aspects of the suspension controlcalibration as described hereinabove particularly in as much asincreased data manipulation affords additional opportunity for datacorruption.

The invention has been described with respect to certain exemplaryembodiments. However, it is to be understood that various modificationsand alternative implementations of the invention may be practicedwithout departing from the scope of the invention as defined in thefollowing claims.

1. Apparatus for indicating vehicle driving condition states comprising:a memory device including predetermined bit positions for storing binarycodes of a predetermined bit length, the bit length describing aquantity of bits in each of the stored binary codes; and a computerbased controller configured to: monitor an input describing stability ofthe vehicle; determine at least one valid binary code corresponding to avehicle driving condition state comprising understeer and oversteerbehavior of the vehicle based upon the monitored input; and control avehicle stability control system based upon the valid binary code;wherein each valid binary code comprises a series of bit states, eachbit state represented by a one or a zero, and is characterized by apredetermined ratio of corresponding bit states, the ratio describing anumber of bit states equaling one and a number of bit states equalingzero and being a fixed value and common to all of the valid binarycodes; and wherein each valid binary code is differentiated from allother valid binary codes by differences between at least twocomplementary bits of each respective valid binary code, the differencesrequiring two bit transitions in opposite directions for a change in thevehicle driving condition state to be indicated.
 2. The apparatus forindicating vehicle driving condition states as claimed in claim 1wherein the predetermined bit length comprises two bits descriptive ofthe understeer and oversteer.
 3. The apparatus for indicating vehicledriving condition states as claimed in claim 1 wherein said vehicledriving condition state further comprises neutral steer and thepredetermined bit length comprises three bits descriptive of theundersteer, oversteer, and neutral steer.
 4. The apparatus forindicating vehicle driving condition states as claimed in claim 1wherein said vehicle driving condition state further comprises left andright turning and the predetermined bit length comprises two bitsdescriptive of the left and right turning.
 5. The apparatus forindicating vehicle driving condition states as claimed in claim 1wherein said vehicle driving condition state comprises oversteer-left,oversteer-right, understeer-left and understeer-right and thepredetermined bit length comprises four bits descriptive of theoversteer-left, oversteer-right, understeer-left, and understeer-right.6. The apparatus for indicating vehicle driving condition states asclaimed in claim 1 wherein said vehicle driving condition statecomprises oversteer-left, oversteer-right, understeer-left,understeer-right, neutral steer-left and neutral steer-right and thepredetermined bit length comprises four bits descriptive of theoversteer-left, oversteer-right, understeer-left, understeer-right,neutral steer-left, and neutral steer-right.
 7. Apparatus for indicatingvehicle driving condition states in a computer based controllercomprising: a memory device including predetermined bit positions forstoring binary codes of a predetermined bit length, the bit lengthdescribing a quantity of bits in each of the stored binary codes; atleast one valid binary code corresponding to a vehicle driving conditionstate comprising understeer and oversteer behavior of the vehicle basedupon a monitored input; and a calibration memory device having a firstpair of bits corresponding to jounce control and a second pair of bitscorresponding to rebound control for each of the vehicle drivingcondition states and for each of a plurality of independentlycontrollable suspension units wherein a first complementary arrangementof the first pair of bits corresponds to a first jounce controlcalibration, and wherein a second complementary arrangement of the firstpair of bits corresponds to a second jounce control calibration, andwherein the first complementary arrangement of the second pair of bitscorresponds to a first rebound control calibration, and wherein thesecond complementary arrangement of the first pair of bits correspondsto a second rebound control calibration; wherein each valid binary codecomprises a series of bit states, each bit state represented by a one ora zero, is characterized by a predetermined ratio of corresponding bitstates, the ratio describing a number of bits states equaling one and anumber of bit states equaling zero and being a fixed value and common toall of the valid binary codes, and is differentiated from all othervalid binary codes by differences between at least two complementarybits of each respective valid binary code; wherein jounce controldescribes controlling a response to compression through damper controlin the independently controllable suspension units; and wherein reboundcontrol describes controlling a response to extension through dampercontrol in the independently controllable suspension units.
 8. Theapparatus for indicating vehicle driving condition states in a computerbased controller as claimed in claim 7 wherein the calibration memorydevice comprises a non-volatile memory device and the respective firstand second pairs of bits are stored therein in predetermined ones of thefirst and second complementary arrangements.
 9. The apparatus forindicating vehicle driving condition states in a computer basedcontroller as claimed in claim 7 wherein the calibration memory devicecomprises a read-write memory device and the respective first and secondpairs of bits are periodically set therein to ones of the first andsecond complementary arrangements as a function of predetermined vehicleoperating parameters.
 10. Method for indicating vehicle drivingcondition states within a memory device of a computer based controllercomprising: providing a first binary coded variable for conveyingvehicle steering response states wherein valid binary codes share afirst ratio of individual bit states and are differentiated one fromanother by differences between at least two complementary bits;providing a second binary coded variable for conveying vehicle turningdirection states wherein valid binary codes share a second ratio ofindividual bit states and are differentiated one from another bydifferences between at least two complementary bits; and providing athird binary coded variable for conveying vehicle dynamics states basedon combinations of vehicle steering response and turning directionstates wherein valid binary codes share a third ratio of individual bitstates and are differentiated one from another by differences between atleast two complementary bits; wherein the valid binary codes comprise aseries of bit states, each bit state represented by a one or a zero; andwherein the ratios describe a number of bit states equaling one and anumber of bit states equaling zero.
 11. The method for indicatingvehicle driving condition states within a memory device of a computerbased controller as claimed in claim 10 wherein vehicle steeringresponse states comprise oversteer and understeer and the first binarycoded variable comprises two bits descriptive of the oversteer andundersteer.
 12. The method for indicating vehicle driving conditionstates within a memory device of a computer based controller as claimedin claim 10 wherein vehicle steering response states comprise oversteer,understeer and neutral steer and the first binary coded variablecomprises three bits descriptive of the oversteer, understeer, andneutral steer.
 13. The method for indicating vehicle driving conditionstates within a memory device of a computer based controller as claimedin claim 10 wherein vehicle turning direction states comprise left andright and the second binary coded variable comprises two bitsdescriptive of the left and right vehicle turning direction states. 14.The method for indicating vehicle driving condition states within amemory device of a computer based controller as claimed in claim 10wherein vehicle dynamics states comprise oversteer-left,oversteer-right, understeer-left and understeer-right and the thirdbinary coded variable comprises four bits descriptive of theoversteer-left, oversteer-right, understeer-left, and understeer-right.15. The method for indicating vehicle driving condition states within amemory device of a computer based controller as claimed in claim 10wherein vehicle dynamics states comprise oversteer-left,oversteer-right, understeer-left, understeer-right, neutral steer-leftand neutral steer-right and the third binary coded variable comprisesfour bits descriptive of the oversteer-left, oversteer-right,understeer-left, understeer-right, neutral steer-left, and neutralsteer-right.
 16. Method for indicating vehicle driving condition stateswithin a memory device of a computer based controller comprising:determining valid binary codes, each code corresponding to a vehicledriving condition state comprising understeer and oversteer behavior ofthe vehicle, comprising: monitoring an input describing stability of thevehicle; and determining the vehicle driving condition state based uponthe monitored input; providing a memory location within the memorydevice for storing the valid binary codes corresponding to the vehicledriving condition states; storing within the memory location validbinary codes; and utilizing the stored codes to control a vehiclestability control system; wherein each valid binary code has a firstratio of individual bit states, each bit state represented by a one or azero value, the ratio describing a number of bit states equaling one anda number of bit states equaling zero and being fixed and common to allof the valid binary codes, and each valid binary code is differentiatedfrom other valid binary codes by differences between at least twocomplementary bits, the differences requiring two bit transitions inopposite directions for a change in the vehicle driving condition stateto be indicated.
 17. The method for indicating vehicle driving conditionstates within a memory device of a computer based controller as claimedin claim 16 wherein valid binary codes that have no identical adjacentbits correspond to preselected vehicle driving condition statesdesirably having the highest level of security.
 18. The method forindicating vehicle driving condition states within a memory device of acomputer based controller as claimed in claim 16 wherein valid binarycodes that have no identical adjacent bits correspond to oversteerstates.
 19. The method for indicating vehicle driving condition stateswithin a memory device of a computer based controller as claimed inclaim 17 wherein preselected vehicle driving condition states desirablyhaving the highest level of security comprise an oversteer vehicledriving condition state.
 20. The method for indicating vehicle drivingcondition states within a memory device of a computer based controlleras claimed in claim 17 wherein the preselected vehicle driving conditionstates desirably having the highest level of security correspond to anoversteer vehicle driving condition state.
 21. The method for indicatingvehicle driving condition states within a memory device of a computerbased controller as claimed in claim 17 wherein vehicle drivingcondition states further comprise neutral steer states, and thepreselected vehicle driving condition states desirably having thehighest level of security correspond to an oversteer vehicle drivingcondition state.